Setting the current style from the UI is a mode that is cancelled when moving away

Setting the current style from the UI is a mode that is cancelled when moving away
from the current caret position. This must be done to avoid confusing default
attributes and attributes at the current caret position, in normal use.
Style feedback now correct when caret is at the start of a paragraph (don't use
previous paragraph's style), and out-by-one style feedback bug fixed (start/end
of styled content).
Added ApplyStyle for applying a character or paragraph style.
Some coding style cleanup.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@41169 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775